Wow! Treeki, that's awesome. Keep up the good work.
I may be hacking NSMB Wii someday if you succeed to find a way to play modified levels with the original disc. I hope you'll do.
Otherwise, that means people need a modchip to run their edited levels, or use Dolphin which seems still slow according to the videos I could see.
Unless it is possible to run the modified game using the homebrew channel or some other exploit.
One way of playing edited levels with the original disc could be some kind of loader you'd run from the homebrew channel, then loads the game in memory exactly like the WiiOS would do, and changes the levels in memory before running the game...
But the game may be reading the levels directly from the disc. In this case you'd need something like a custom IOS, that would intercept reads to the level files in the disc and redirect them to the edited level files.
Anyway, keep up the good work Treeki!